1. Field of the Invention
The present invention relates particularly, though not solely, to the delivery of high flow humidified pressurized oxygen and/or air to a patient in need of respiratory support by way of a nasal cannula
2. Description of the Related Art
Nasal cannula generally consist of entry tubing, either symmetric or single sided that lies across the upper lip. Protruding from this tubing are open ended prongs which extend into the nares of the patient to deliver oxygen. Nasal cannulae have the advantage of being more comfortable and acceptable than a facemask to most patients. The existing market for nasal cannula is well serviced by devices suitable for the delivery of gases in the 0 to 5 liter per minute range. These devices are typically supplied by a double entry lumen of small diameter (2-3 mm range) that supplies both sides of the nasal cannula and provides even airflow to each nasal prong. These devices work well for the delivery of low humidity gas flows of between 0 to 5 liter per minute and have been well received by patients over the last 30 years.
Hudson Respiratory Care Incorporated manufactures a nasal cannula that is disclosed in U.S. Pat. No. 2,868,199 that consists of a single flow entry nasal cannula. This single flow entry has the advantage of being unobtrusive, and more relevant to delivering humidity than a dual flow entry style of nasal cannula, simply due to the advantage of flow rates and surface area for heat loss. The single flow entry is on the left side only, which causes the user difficulty in use if the flow source is on the opposite side of the user requiring longer lengths of tubing and causing the tube to cross the body. The cannula itself is manufactured as one part only, of PVC plastic. This product is not designed for delivering high flow or high humidity gases. The nasal prongs are less than 3 mm in diameter resulting in noise and high velocity jetting of gas causing severe irritation at high flows. These cannulae are difficult to clean inside, are uncomfortable, and the prongs are too rigid for extended therapies.
U.S. Pat. No. 3,754,552 of Sandoz-Wander, Inc. discloses a nasal cannula, having two nasal prongs, adapted for the intake of therapeutic gas from either the right or left side of the patient. Here the nasal cannula has a bore within it that feeds each prong. The bore is able to receive a tube for supplying gases to the cannula in either end and in use a plug is required to obstruct the unused end.
Innomed Technologies, Inc. manufactures a nasal cannula device called the NASALAIRE™. This nasal cannula is a dual flow entry style cannula where two large tubes come from behind the ears, through the field of vision to the upper lip. In this device air or oxygen travels down a wide bore conduit to the nasal cannula. The NASALAIRE™ creates a physical seal between the nares and itself, and relies on the absence of leaks around itself and the nares to deliver pressure supplied by a continuous positive airway pressure (CPAP) blower to the airway of the wearer. The wearer is required to breathe in and out of the NASALAIRE™, thereby rebreathing some of the exhaled air from the lungs. The NASALAIRE™ is not designed to deliver humidified gases to the patient, being unheated and without insulation of any type. The NASALAIRE™ cannula is uncomfortable especially if a patient rests on the tube, as would happen during sleep, and is also obtrusive.
The new application of high airflow extended therapies using nasal cannulae generally result in the nasal cannula reaching temperatures in excess of 35 degrees C. Usually cannulae are made from soft polymeric material (for example, silicone) that absorbs heat and does not breathe and therefore sweat is generated under the contact points with the skin. This heat in combination with the polymeric materials waterproof properties results in sweat being trapped against a patient's skin and the patient has the sensation of overheating. The trapped sweat is uncomfortable and could lead to rashes.
Oxygen is generally supplied as a dry gas, but it is well known in the art to either heat and/or humidify gases before delivering them for breathing by a patient. In particular when delivering oxygen, or an oxygen air mixture, it has proven beneficial to humidify the gases first. In WO 01/41854 of Vapotherm, Inc. a system is disclosed that allows the delivery of humidified oxygen through a nasal cannula. This system uses a narrow bore conduit and nasal cannula with a high resistance to gas flows, thereby requiring the oxygen be of a high pressure. Air, as well as oxygen, can also be passed down the conduit and nasal cannula and it too must be of a high pressure. This system allows the delivery of high flows of oxygen enriched air to the patient, but is limited in the flows achievable due to the narrow bore of the cannula resulting in high resistance gas flow and excessive velocity and noise upon exiting the cannula. Furthermore, the narrowness of the nasal cannula in this system allows the patient to easily expire gases from their nostrils as there is a reasonable gap between the prongs and the patient's nares. Thus positive airway pressure is not created and as such this cannula is not suitable for the treatment of Obstructive Sleep Apnea (OSA).
In breathing circuits that supply respiratory gases to a patient by way of a patient interface, such as a nasal cannula, mask or tracheal tube, it is common to have a heated breathing circuit or tube delivering heated and humidified gases to the patient, followed by a short length of non-heated tube close to the patient. This unheated tube may be a short unheated extension tube or catheter mount. The unheated section of tube is usually intended to be very flexible to reduce torsion or pulling on the patient interface, to allow the gases to cool slightly towards the dew point of the gas, and also to eliminate hot surface temperatures near the patient. As this tube is unheated the temperature of the tube walls are colder than the dew point temperature of the gas, as a result the vapor in the gases passing near these walls will begin to condense out. Over time a build up of condensate close to the patient may lead to a build-up of bacteria which may cause infection. Build up of condensation may also create noise, such as gurgling, which may wake a patient, and in extreme circumstances the fluid build up may cause drowning.
When providing humidified gases to a patient it is common to use a heated breathing circuit (tubing). This circuit is heavy and can drag and pull on the patient interface. This is more pronounced if the patient is mobile and can be painful and/or dangerous if the patient interface is invasive such as an endotracheal tube. It is common to use a short flexible tube between the heated circuit and patient interface to reduce any torque or twisting. In order to stop the weight pulling on the patient interface, circuit hangers are occasionally used. This is a large extendable metal arm to take the weight. It also has been known in the art to clip part of the tubing to the patient's clothes or bedclothes. Both of these solutions have been found to be quite unsuitable for mobile patients especially when sleeping and turning in bed.
With patient interfaces such as nasal cannulae the stability of the nasal prongs on the face is very important, as movement of the prongs within the nares can cause severe irritation. Current methods employed to retain a single entry nasal cannula on the face use a simple elastic band of material around the back of the patients head. This is prone to rotating the nasal cannula relative to the patient's head especially when turning ones head on a pillow. This rotation causes the prongs move within the nares, irritating this sensitive area.